Based on your fine detail work, I would suggest that the shock angle is relative to the lower a-arm in the calculator.
I know in most streetrod setups with IFS, the lower a-arm is usually considered to be lever with the road in normal standing setup.
I believe that some have let their shocks extend out a bit and lowering the outer lower a-arm at the spindle. I think some did this in the old days to help the adverse bump steer issues the M3W had.
